The present invention relates to alignment and position sensing of locks and other objects. While the invention is applicable to different types of objects, some aspects of the invention were motivated by electronic deadbolt locks.
Unlike spring bolts which are spring-biased into an extended (locked) position, a deadbolt is not biased, and has to be extended by turning a key or a knob or, in electronic operation, by an electro-mechanical actuator (e.g. motor, solenoid, etc.). When a door with a spring-bolt lock is being closed, the door jamb pushes the spring bolt into the door and the spring bolt retracts. In contrast, the deadbolt does not need to retract when pushed against the door jamb, and therefore deadbolts can be heavier and stronger to provide greater security against lock picking.
U.S. Pat. No. 4,744,021 issued May 10, 1988 to Kristy describes a computer-controlled electronic deadbolt for a vehicle door. A computer-controlled motor extends or retracts the deadbolt in response to a push-button-activated signal from a transmitter. When the deadbolt meets an obstruction while being extended or retracted, the motor slows or stops, and the motor's current flow increases. This condition is sensed to energize an obstruction indicator such as a buzzer.